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Benchmarking Techniques for Stereotactic Radiosurgery to Multiple Brain Metastases with One Isocenter: Multi-Aperture Dynamic Conformal Arcs Vs. VMAT

T Li

T Li*, W Shi , Y Yu , H Liu , Thomas Jefferson University, Philadelphia, PA


SU-K-FS1-6 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: Four Seasons 1

Purpose: To compare an automatic brain metastases planning system using multi-aperture dynamic conformal arcs to VMAT technique for single-isocenter-multi-target SRS.

Methods: 10 patients each with 6-10 brain metastases were retrospectively studied. All patients were planned and treated with an automatic brain metastases planning (ABMP) system (Brainlab) based on dynamic conformal arcs with multiple aperture openings simultaneously. The ABMP plans were imported into Eclipse™ treatment planning system (Varian), followed by recalculating dose using AcurosXB algorithm. For each patient a VMAT plan was also developed with the same Rx, isocenter, and dose calculation algorithm. Both ABMP and VMAT plans were normalized so that all targets receive ≥99% coverage by their Rx doses. Comparisons between ABMP/VMAT include RTOG conformity index(CI) for all targets, max doses, OAR dose indices, total MU, total degrees of arc rotation. Wilcoxon signed rank test was used to determine statistical significance in paired comparison.

Results: Lesion sizes ranges from 0.12cc to 8.59cc, averaging 1.59±2.29cc. CI using ABMP were inferior (1.76±0.52) compared to VMAT (1.27±0.28). On average ABMP irradiates 38±29% more tissue to Rx dose than VMAT. Max dose by ABMP were also higher than VMAT (127.3±8.0% vs. 119.6±3.9%). Brain volumes receiving 12Gy and 6Gy are not significantly different (p>0.15); but ABMP reduced low dose spillage (V3Gy) by 10±12.3% (p=0.05). Differences in maximal doses to brainstem, optical nerves, and chiasm were all insignificant (p>0.05). For MU efficiency, ABMP plans reduced MU by 19±10% compared to VMAT (p=0.002), but increased total length-of-arc by 490±143 degrees.

Conclusion: When compared to VMAT, the multi-aperture dynamic conformal arc technique improved low dose spillage and required substantially less MU, at the cost of inferior dose conformity. Target coverage and other OAR dosimetry were similar. The trade-off between dose conformity and MU/low dose spillage is the key factor to consider when deciding between these two techniques.

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